CO2 hydrogenation to methanol over ceria-zirconia NiGa alloy catalysts

NiGa alloy particles supported on CeO2, ZrO2 and ZrO2-CeO2 solid solutions are prepared, characterized, and utilized for hydrogenation of CO2 into methanol. The nature of the support, including the Zr:Ce ratio, affects the catalyst structure and properties such as the ZrO2 crystalline phase, number of basic sites and concentration of oxygen vacancies. At high Zr:Ce ratios, the crystalline structure of ZrO2 has more influence on the catalytic activity than the oxygen vacancies introduced by the addition of CeO2, with the pure ZrO2 having the highest methanol selectivity of 53% with a CO2 conversion of 2.1% at 260 degrees C and 600 psi. In the equimolar and Ce-rich catalysts with a tetragonal ZrO2 crystalline phase, basic sites, and oxygen vacancies are the parameters most influencing the methanol production. The highest methanol productivity was obtained for the Zr5Ce5 supported catalyst, with a selectivity of 46.8% and a CO2 conversion of 2.7%. Overall, the space time yield of methanol is shown to correlate linearly with the concentration of moderate basic sites. The catalysts possess low activity relative to comparable systems utilizing metallic Cu phases, in part due to low NiGa dispersions achieved using the synthetic methods employed here.